# [R] number to volume weighted distribution

PIKAL Petr petr.pikal at precheza.cz
Fri Nov 24 14:30:01 CET 2017

Hi Duncan

I tried Ecdf and/or wtd.quantile from Hmisc and it is working (probably).
Ecdf(x, q=.5)
wtd.quantile(x)
0%  25%  50%  75% 100%
10   10   10  100  300
wtd.quantile(x, weights=xw, type="i/n")
0%      25%      50%      75%     100%
10.0000 138.8667 192.5778 246.2889 300.0000

But could you please be more specific in this?

> definition rather than a function:  it is obtained simply by normalizing the
> weights to sum to 1, then evaluating cumulative sums of them.

Actually, when I correctly calculate weights

xw <- (x^3)/sum(x^3)
sum(xw) equals to 1

but how can I plot ecdf with volume weighted data. Obviously

ecdf(x*xw) or ecdf(x^3*xw) is not correct.

Cheers
Petr

> -----Original Message-----
> From: Duncan Murdoch [mailto:murdoch.duncan at gmail.com]
> Sent: Friday, November 24, 2017 12:36 PM
> To: PIKAL Petr <petr.pikal at precheza.cz>; r-help at r-project.org
> Subject: Re: [R] number to volume weighted distribution
>
> On 24/11/2017 6:27 AM, PIKAL Petr wrote:
> > Dear all
> >
> > Strictly speaking it is not R question but as you are the most capable persons I
> know I give it a try.
> >
> > I am strugling with recalculation of number weighted to volume weighted
> distribution.
> >
> > Suppose I have objects (cubes) with size
> >
> > x<- c(rep(10,20), rep(100, 10), rep(300,5)) I can get
> >
> > plot(ecdf(x))
> >
> > or the number weighted average
> >
> > mean(x)
> > [1] 77.14286
> >
> > or volume weighted average
> > weighted.mean(x, (x/sum(x^3)))
> > [1] 204.4444
> >
> > However I am struggling with volume weighted ecdf.
> >
> > Can you please give me some hints?
>
> I believe base R doesn't have a function for this, but Google says it exists in a
> couple of packages:  spatstat, Hmisc.  But you seem to be asking about a
> definition rather than a function:  it is obtained simply by normalizing the
> weights to sum to 1, then evaluating cumulative sums of them.
>
> Duncan Murdoch

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